Robot arms with end effectors are used to pick and place semiconductor wafers. The end effectors may typically be a “blade” type end effector, e.g., spatula-like. Many blade-type end effectors rely on gravity and friction to hold the semiconductor wafer in place and moving the end effector too quickly may cause the semiconductor wafer to slip off the end effector. One conventional approach is to utilize a sensor or sensors to detect when the semiconductor wafer is no longer on the end effector, e.g., the wafer has fallen off, and to stop the robot arm when such an event has occurred.